Showing papers on "Fluence published in 1977"

Photon energy distribution of some typical diagnostic x‐ray beams

Abstract: A high-purity germanium spectrometer system was used to determine primary x-ray spectra over the 45--90-kVp region. Methods were devised for producing and examining spectra stimulating diagnostic conditions without operating the x-ray generator at high current levels. The techniques used to correct the experimental data and produce a photon fluence spectrum are discussed. The results, presented graphically and in tables, have been normalized to yield the relative number of photons per 2-keV interval. Methods for converting a normalized spectrum into a photon fluence spectrum that will produce an exposure of 1 R are presented. The analytical model and procedures used to calculate the K-escape fraction are discussed.

High fluence deuteron bombardmemnt of silicon

Abstract: A study has been made of d+ ion implantation in Si(111) at 100 K and 300 K. Deuterium depth profiles as a function of fluence were obtained using a method based on observing the energy spectra of the tritons and protons from the D(d, p)T reaction induced with a deuteron beam. Profiles at 300 K show two distinct regions in the target. For a fluence of 4 × 1015 d+/cm2 the surface region which extends over the first half of the deuteron range contains little deuterium (∼ 0.3 atomic %) while a relatively large amount (∼ 5 at. %) is retained in a buried layer. Typical scanning electron micrographs taken following implantation are presented. They show the deeper layers to be highly damaged. In striking contrast, the surface region shows little observable damage even for doses exceeding 1019d+/cm2. Deuterium diffusion coefficients are estimated for silicon under irradiation conditions.

Damage production by high-energy d-Be neutrons in Cu, Nb, and Pt at 4.2 °K

Abstract: Electrical resistivity measurements have been used to observe damage production rates for Cu, Nb, and Pt irradiated with high‐energy d‐Be neutrons at 4.2 °K. The neutrons were generated at the Oak Ridge Isochronous Cyclotron by the reaction of 40‐MeV deuterons incident on a thick Be target. The resulting neutron energy spectrum was broadly peaked near 15 MeV. Damage production was proportional to fluence up to 4×1015 n/cm2, and was approximately three times greater than for the same fluence of fission neutrons in these materials. This result is in good agreement with predictions based on damage energy calculations.

Optically induced charge storage in ion implanted SiO2

Abstract: Charge storage in MOS structures with an ion implanted oxide layer has been investigated. The electrons generated by internal photoemission are captured in SiO2 traps which are created by the implantation of Kr+ and N+ ions at energies of 50–290 keV and a fluence up to 1014 cm−2. The charge storage results in a voltage shift of the high frequency C-V-curve. The dependence of electron storage on exposure time has been measured and compared with approximative calculations. The discharge of traps occurs by heating treatment and hints at the existence of deep oxide traps combined with structural lattice defects.

Response of tissue‐equivalent ionization chamber to l5‐MeV neutrons

Abstract: The calibration (in rad/nC) of an air-filled tissue-equivalent ionization chamber for neutrons of l5-MeV average energy was determined by measuring absolute fluences and calculating the kerma per unit fluence. The neutron calibration determined from the ..gamma..-ray calibration and application of the Bragg--Gray relation was found to be 4% higher than that based on the fluence measurement. Additional data were taken to obtain calibration factors with tissue-equivalent gas; the same difference betwen the two methods was observed.

Radiation Damage of 50–250 keV Hydrogen Ions in Silicon

Abstract: Damage distributions in [001] Si crystals bombarded with a fluence of 1016 to 1017/cm2 at 50 keV to 250 keV H+ ions at temperatures below 600° C were measured using high energy He+ channeling. The nature of the damage was investigated by transmission electron microscopy (TEM). Different defect types are formed at different target temperatures, e.g. microblisters located on {111} planes exist between 100°C and 450°C. With higher fluences or post-implantation anneal the Si surface becomes visibly blistered.

Creep-Rupture Properties of 20% Cold-Worked Type 316 Stainless Steel after High Fluence Neutron Irradiation

Abstract: (1977). Creep-Rupture Properties of 20% Cold-Worked Type 316 Stainless Steel after High Fluence Neutron Irradiation. Nuclear Technology: Vol. 35, No. 1, pp. 9-11.

Reactor irradiation induced changes in the electrical properties of SnO 2 thin films

Abstract: Undoped evaporated SnO2 thin films 30 … 1000 A thick were irradiated in a reactor up to fast neutron fluence of 7 × 1017 n/cm2 at 80 K and 350 K temperatures. The irradiation induced changes in electrical resistivity and the Hall coefficient were measured at various stages of irradiation. At 80 K the resistivity increased nearly 3 decades with no saturation in the fast neutron fluence obtained. During the 350 K irradiation periods saturation was observed to start at the fluence of 2 … 3 × 1017 n/cm2 the resistivity increasing only to a value of twice the original resistivity. The results could be explained by irradiation induced disordered regions surrounded by space charge which hinder the current conduction inside the material.

High Power Laser Coupling

Abstract: A pulsed chemical laser has been developed for laser effects studies. The threshold conditions for forming absorbing plasmas at atmospheric pressure have been studied at both hydrogen fluoride (HFJ and deuterium fluoride (D(9 wavelengths and for seven materials. These plasma-production thresholds were obtained by measuring the laser power transmitted through a small hole in the target and have been determined in terms of both irradiance and fluence requirements,, The plasma spreading magnitude has been measured as a function of laser-delivered energy and for both wavelengths0

Internal Friction Study of Vacancy-Oxygen Centers in Ion-Implanted Silicon

Abstract: Thin reeds of oxygen-implanted silicon vibrating near 400Hz exhibit an internal friction peak close to 200°K, which has been shown to originate from the stress-induced reorientation of vacancy- oxygen (V-O) centers. The peak has been used to study the production of these centers in 100 and 200 keV oxygen-implante float-zoned silicon over the fluence range 1014 to 5×1016 0+ /cm2. Peak broadening, present even at the lowest fluence, indicates a damage- induced perturbation of the crystalline environment containing the defects; however the average activation energy for defect reorientation (0.38 eV) is the same as that for less heavily damaged electron-irradiated samples. The strength of the increases sublinearly with fluence over the range 1014 to 1015 0+ /cm2 and subsequently passes through a maximum near the fluence at which a continuous amorphous layer is formed. At a fluence of 1014 0+ /cm2 about one-third of the implanted oxygen ions are detected as V-O centers. This fraction decreases rapidly in the fluence range where the amorphous layer form and thickens, and is only two per thousand for a fluence of 5×1016 0+ /cm2.

Magnetic compression and electrostatic reflection of very high /spl upsi/ γ electron beams

Abstract: High current sub-ohm electron-ion diodes are produced in the highly converging fringe fields at one end of a magnetic solenoid. With these diodes, the magnetic compression of a very high /spl upsi/γ electron beam is investigated with and without the formation of a virtual cathode at the peak magnetic field. The magnetically focused beam transmission efficiency, area compression, and fluence gain are documented for up to 10:1 mirror ratios. When a virtual cathode is formed at the mirror peak, efficient electron beam reflexing is induced - thereby increasing the effective fluence through thin foils by a factor of six (or twice the optimum gain with conventional magnetic compression). Up to 3 MJ/g deposition in 0.1 mil copper foil is deduced from this data.